Heat developable photographic light-sensitive materials and a process for forming images using the materials are well known and are described in detail, for example, in Shashin Kogaku no Kiso (Fundamentals of Photographic Engineering), pp. 553-555 (Corona Co., Ltd., Tokyo, 1979); Eizo Joho (Image Information) p. 40, April, 1978, and Neblette's Handbook of Photography and Reprography, PP. 32-33, (Van Nostrand Reinhold Company, 7th Ed. (1977)). For the formation of, in particular, color images, various techniques have been proposed, including a method in which couplers are used as dye providing substances (see U.S. Pat. Nos. 3,531,286, 3,761,270, 4,021,240, Belgian Pat. No. 802,519, and Research Disclosure, September, 1975, pp. 31-32), a method in which compounds with a nitrogen-containing heterocyclic ring group introduced in the dye portion are used as dye providing substances (see Research Disclosure, May, 1978, pp. 54-58), a method utilizing the silver dye bleaching process (see Research Disclosure, April, 1976, pp. 30-32, ibid., December, 1976, pp. 14-15, and U.S. Pat. No. 4,235,957), and a method utilizing leuco dyes (see U.S. Pat. Nos. 3,985,565 and 4,022,617).
These methods, however, have their respective disadvantages. Their common disadvantages are that the development requires relatively long periods of time, images formed have undersirably high fog levels, and the maximum density (D.sub.max) is low.
In order to overcome the above problems, Japanese Patent Application (OPI) No. 58543/83 (corresponding to U.S. Pat. No. 4,500,626) (the term "OPI" as used herein refers to a "published unexamined patent application") discloses a method using dye providng redox compounds which release hydrophilic dyes. Although this method has succeeded in ameliorating the above disadvantages, it has been desired to obtain a light-sensitive material which can be heat developed at relatively low temperatures, and in short period of time, and in which a high maximum density can be obtained while preventing the formation of fog.